Electrical contacting device



March 30, 1943. A. J.- KERCHER ELECTRICAL CONTACTING DEVICE Filed July 29, 1940 Sheets-Sheet 1 'u" in "N n I 'FJLE -l INVENTOR Ar/hur J- L er'cher' March 30, 1943. A. J. KERCHER 2,314,989

ELECTRICAL CONTACTING DEVICE Filed July 29, 1940 2 Sheets-Sheet 2 FIIE El INVENTOR Ar/hur Herc/76F BY WWW ATTORNEY Patented Mar. 30, 1943 UNITED STATES PATENT OFFICE ELECTRICAL CONTACTING DEVICE Arthur J. Kercher, Berkeley, Calif.

Application July 29, 1940, Serial No. 348,110 9 Claims. (01. zoo- 131) This invention relates generally to electrical contacting devices such as are employed for the purpose of controlling various electrical circuits. The invention applies particularly where it is desired to secure a rapid opening and closing movement of electrical contacts in response to relatively small operating movements, as for example where contacts are being opened and closed in response to forces applied from a thermostatic element.

It is an object of the invention to provide simplified apparatus of the above character, which will retain desired adjustments over long periods of time, and which will aflord the desired positive rapid movement of electrical contacts between open and closed positions.

Another object of theinvention is to provide adjustable means which can be set as the apparatus is assembled at the time of manufacture, whereby the parts may be manufactured without regard-to extreme accuracy.

Another object of the invention is to provide an improved manner for mounting the contacts of such electrical contacting devices.

Additional objects of the invention will appear from the following description in which the preferred embodiment of the invention has been set forth in detail in conjunction with the accompanying drawings.

Referring to the drawings:-

Figure 1 is a side elevational view, illustrating a thermostatically controlled switch incorporating the present invention;

Figure 2 is a top plan view of the apparatus shown in Figure 1;

Figure 3 is a. cross sectional view on an enlarged scale taken along the line 3-4 of Figure 1;

Figure 4 is a cross sectional detail, on an enlarged scale, taken along the line 4-4 of Figure- 2;

Figure 5 is a cross sectional detail, on an enlarged scale, taken along the line 55 of Figure 2;

Figure 6 is an enlarged cross sectional detail taken along the line 8-8 of Figure 2;

Figure '7 is a side elevational view, partly in cross section, showing another embodiment of the invention, in which two contacting devices are employed for operation by a single thermostatic unit; and

Figure 8 is a cross sectional detail taken along the line 8-8 01 Figure 7.

The apparatus illustrated in Figures 1 to 4 inclusive is in the form of a thermostatic switch,

operated changes. The operating partsare carried by a mounting plate ill, and they include the thermostatic element A and the contacting device B.

One of the principal parts of the contacting device B is the strip H which is formed of suitable spring metal, such as hardened spring steel or phosphor bronze. One end portion lid of this strip is anchored to the fixed support ID, as by adjustable means such as will be presently described. An adjacent portion lib is formed as an integral loop, thus affording an interposed resilient portion. The ire end portion He can move in opposite directions, and is operativeiy connected to electrical contact elements. That portion of the strip intermediate the free end He and the looped portion no is cut away to form an integral tongue l2. The free end of this tongue is beveled to iorm a knife edge which normally engages the fixed abutment i3. That portion lid of the strip which lies intermediate the free end of tongue i2 and the looped portion lib is adapted to receive operating forces from the thermostatic device A.

The anchoring of the strip portion iia. to the fixed support I0 is such that the looped portion ilb is normally stressed a predetermined amount within its elastic limit. As will be presently explained, this makes possible a snap action of the strip. The anchorage to the mounting plate i0 is preferably such that the stress applied to the portion ilb can be adjusted at the time of assembly. Thus an eccentric bushing i6 is rotatably retained within an opening il in the strip portion Ila. A stud l8 extends through bushing i6 and has threaded engagement with the pad is, which in turn is mounted upon plate it). At the time of assembly, bushing 16 can be adjusted to an angular position such as will afiord the desired degree of tension upon the looped portion lib, or in other words to urge the tongue i2 with a predetermined amount of force against the fixed abutment i3. Thereafter the stud I8 is turned down to tightly clamp bushing l6 and strip portion Ila upon the pad 19, and to hold the bushing in its adjusted position.

For the mounting of certain parts of the contacting means, there is a plate 2i disposed parallel to the plate I!) and carried by the spacing studs 22, The two sets of terminals 23 and 24, carried by plate 2i, are for making electrical connection with an electrical circuit. A pair oi electrical contact elements 26 are directly connected to terminals 24, and are disposed upon the inner face of plate 2|. A pair of movable in accordance with temperaturecontacts I! are adapted to make engagement with contact elements 23, and they are carried upon the ends 01' an insulating strip 33. The central part of strip 23 carries a stud 3| provided with a groove 32. The free end of strip H is provided with a slot 33 to loosely accommodate stud 3|, thus forming a lost motion connection between the free end of the strip H and the strip 23. Contacts 21 are electrically connected by flexible leads 34, with the terminals 23. These leads also serve to retain the strip 33 substantially at right angles to the length 01' strip II.

In some instances it is desirable to apply a bias to continuously'urge the strip il in one direction, as for example in a direction to close the contacts. For this purpose I have shown a small permanent electromagnet 33 mounted upon the insulating plate 2|. The poles oi this magnet act upon a magnetic armature 31, mounted upon the middle part oi the strip 23. In place of such an electromagnet, a biasing spring can be employed.

The thermostatic means incorporated in the structure of Figures 1 to 4 inclusive consists of a metal tube 38, one end of which is secured to the mounting i0. Within this tube there is a rod.

39, one end of which is attached to the free end of tube 33, as by means of a screw or stud 4|. The other end of rod 33 has a threaded engagement with thrust member 42, which in turn carries the pointer 43.

To form an operative engagement between rod 39 and the resilient strip ID, the strip is apertured to receive the rod, and is provided with a bushing 44. The upper face of bushing 44 is spherical shaped to form a concave seat for engaging the adjacent spherical shaped end portion of member. Tube 33 and rod 33 are formed of metals or alloys having diflerent thermal coeflicients of expansion. For example, tube 38 can be of a metal or alloy having a substantial coefllcient of expansion, while rod 33 can be of material having substantially no coeflicient of expansion. Assuming that the tube 38 is immersed in water, or in a fluid medium being heated, an increase in temperature causes elongation of the tube, with the result that rod 39 transmits motion to resilient strip II to flex this strip downwardly as viewed in Figure 4.

A simple temperature scale 41 has been provided upon plate 2| so that one may manually set the device for dlflerent temperature levels 01 operation. It will be evident that the threaded engagement between member 42 and rod 33 varies the relative positioning of rod 33 with respect to the resilient strip H, as the pointer 43 is manually rotated.

In order to insure a minimum amount of heating of the contacts 21, it is'desirable to use a mounting for these contacts such as shown in Figures 5 and 6. In this instance the lead conductors 34 are formed of woven or braided wire ribbon, and one end of the ribbon is inserted between a contact element 21 and its associated mounting rivet 48. This assembly is brazed or soldered together, so that current flow occurs.

directly from the contact element 21 to the lead conductor 34. In practice, the braided conductor can be first soldered or brazed to the back face of the contact element, and then "this assembly in turn brazed or soldered to the mounting rivet 48. In accordance with established practice, the contact elements II are formed of suitable metal or metal alloy having high conductivity, and capable of resisting burning or pitting.

The device described above operates as follows: It will be presumed that the device is set for a given temperature level of operation, and that the terminals 23 and 24 connect in a circuit for supplying current to i heating element, which in turn heats a fluid such as water in thermal contact with the tube 33. Assuming that the temperature of rod 33 is above the temperature level for which the device is set, the railient spring strip II will occupy the position shown in Figure 4, with the contacts in open position, and with the free end of tongue I! slightly above the plane oi the adjacent portions 01' the resilient strip. Also, the free end lie of the resilient strip will be in its lowermost position, as shown in Figure 4. Now as the temperature. of rod 33 reaches approximately the temperature level oi operation. the spring strip II will be permitted to flex upwardly, under the urge of magnet 33 or other biasing means, until the strip passes dead center position. Dead center position corresponds to that position of tongue I! in which it is in the same plane asthe adjacent portions of the resilient strip. The free end oi the spring strip then snaps upwardly, as viewed in Figure 4, to rapidly close the contacts 21 upon the stationary contact 23. Assuming now that the fluid in thermal contact with rod 33 is being heated by current flow to the electrical heating element, when a predetermined elevated temperature is rached, .rod 33 and the resilient spring strip are pulled downwardly to such an extent as to snap it past dead center position back to the position shown in Figure 4. The lost motion connection between the iree end lie of the resilient spring strip and the stud 3| is such that the contacts are not moved toward open position until after the resilient spring II has been flexed sufliciently tar to secure the desired snap action, that is, past its dead center position. In other words, the latitude of lost motion between the free end lie 61 the spring strip and stud 3| is ample to accommodate the movements of the free end of tongue I! which must occur to obtain rapid snap action.

It will be evident that the apparatus described above makes use or relatively simple means to secure the desired snap action, and in addition forces of relatively small magnitude and movements of relatively small increments can be relied upon to secure movement of the strip past dead center position. Thusthe device is particularly adapted for use in conjunction with thermostatic elements, where the necessity of using forces oi considerable magnitude may cause serious inaccuracies. Also in the present instance the temperature margin between oil and on positions of the contacts may be made relatively small.

The resilient spring strip is so formed that it can be readily manufactured in large quantities, and any inaccuracies in manufacture can be readily compensated for during assembly, because 0! the adjustable anchorage oi-one end of the strip to the plate ll.

Figures 7 and 8 show an embodiment oi the invention in which two contacting means are employed for sequential operation. Thus in this instance the mounting plate Ii corresponds to the plate I0 01 Figures 1 to 4 inclusive, and carried by the plate II are the two insulating plates 32 and 43. The thermostatic element makes use or a Sylphon tube 54, one end oi which is mounted to plate II, as by means of sleeve 56. An inner rod 51 extends through sleeve 56 and Sylphon tube 54. Expansion or contraction of the gas or other fiuid within the tube 64 serves to move rod Bl in opposite directions. Nut 58 threaded upon rod 51 forms an operating attachment to one resilient spring strip 59, while another nut BI is also threaded to rod 51, and is connected to the additional spring strip 62. Spring strips 59 and 62 are constructed and are mounted substantially the same as strip H for Figures 1 to 4 inclusive. One set oi! movable contacts 63 operated by the strip 59 are adapted to close upon the stationary contacts 84 carried by plate 52. Connections can be made to these contacts through the terminal tabs 66. I

Resilient spring strip- 62 is shown operating double or bonded contacts 61 and 68, whereby contact 61 cooperates with the stationary con- .tact 69, and contacts 68 cooperate with the contacts H which are on the upper side of plate 52,

and which are directly bonded to contacts 64..

Assuming that the Sylphon tube 54 is set for a given temperature level or operation for the spring strip 59 and contacts 63, it will be evident that the device can be set for a somewhat different temperature level of operation for, strip 62, by

varying the setting of nut 6!. For example, the setting may be such that contacts 63 are closed upon contacts 64 at a temperature of about 150, and so that if the temperature continues to tail to a value of say 140, contacts 61 will also be closed upon contacts 69. Such sequential operation is frequently desirable in the control of various electrical heating appliances, as for example in conjunction with electrical air heaters where the current supplied to various heating elements is being controlled in accordance with the temperature of the air.

I claim: v

1. In electrical contacting apparatus of the type described, a fiat strip oi. spring metal, the strip being provided with an integral looped Portion near one end of the same, means serving to anchor said one end of the strip to a fixed support, whereby the other end of the strip is free for movement in opposite directions, a part of the strip intermediate the ends of the same bein cut away to form a spring tongue with the free end of the tongue extending toward said one end, a fixed abutment serving to engage the free end of the tongue, whereby said loop is stressed to afiord snap action for the strip past dead center position.

2. In electrical apparatus of the type described, a flat strip of spring metal, the strip being provided with a resilient portion near one end of the same, means serving to anchor said one end'to a fixed support, the other end of the strip being free for movement in opposite directions, movable electrical contacting means, means forming an operative connection between said contacting means and the free end of the strip, a part oi the strip intermediate the ends of the same being cut away to form a spring tongue, with the free end of the tongue extending toward said fixed support, a fixed abutment serving to engage the iree end of the tongue whereby said resilient portion is stressed within its elastic limit, thereby afifording snap action for the free end of the strip.

3. In electrical contacting apparatus of the type described, a fiat strip of spring metal, the strip being provided with a resilient looped portion near one end of the same, means serving to anchor said one end to a fixed support, with the other end of the strip free for movement in opposite directions, electrical contacting means, an operative connection betweenthe free end oi. the strip and said electrical contacting means, a part of the strip intermediate the ends of the same being cut away to form a spring tongue, with the free end or the tongue extending toward said fixed support, a fixed abutment engaging the free end of the tongue whereby said resilient looped portion is stressed within its elastic limit to afiord snap action for the strip, and means for applying operating forces to that portion of the strip intermediate said looped portion and said fixed abutment.

4. In electrical contacting apparatus of the type described, a fiat strip of spring metal, means serving to anchor one end of the strip to a hired support, the other end of the strip being free for movement in opposite directions, a movable electrical contact, means forming a lost motion connection between the free end of the strip and said electrical contact, and means causing snap action of the strip, whereby said contact is moved rapidly between limiting positions of the same.

5. In electrical contacting means of the type described, a flat strip of spring metal, the strip being provided with, an integral looped portion near one end of the same, said looped portion extending across the width of the strip at right angles to the length of the strip, means serving to anchor said one end of the strip to a fixed support, whereby the other end of the strip is free for movement in opposite directions, electrical contacting means operatively connected to the free end of the strip, a part of the strip intermediate the free end oi the same and said looped portion being cut away to form a spring tongue, the base of the tongue being near the free end of the strip, and the free end of the tongue extending toward said looped portion but terminating short of the same, a fixed abutment engaging the freeend of the tongue and serving to stress said looped portion within its elastic limit, thereby causing snap action of the strip.

6. In electrical contacting apparatus of the type described, a flat strip of spring metal, the strip being provided with a resilient looped portion near one end of the same, means serving to anchor said one end of the strip to a fixed support, with the other end of the strip being free {or flexing movement in opposite directions, electrical contacting means operatively connected to the free end of the strip, that portion of the strip intermediate the free end of the same and said resilient portion being cutaway to form a spring tongue, the free end of the spring tongue extending toward the fixed support and terminating short of said resilient portion, a fixed abutment engaging the free end of the tongue whereby the looped portion is stressed within its elastic limit to afford snap action for the strip, and a temperature responsive means for applying operating forces to that portion of the strip intermediate said fixed abutment and said resilient portion. 7

'7. In electrical contacting apparatus of the described, a flat strip of spring metal, means serving to anchor one end of the strip to a fixed support. whereby the other end of the strip is free to move in opposite directions, contacting means operatively connected to the free end of the strip, said contacting means comprising a pair of electrical contacts, a mounting strip having said contacts carried by the ends of the same, means forming a loose connection between the central portion of said mounting strip and the free end of said spring metal strip, flexible current carrying conductors connected to the contacts, and means serving to anchor the other end of the current carrying conductors to a fixed support, whereby said mounting strip is maintained in a position substantially at right angles to the length of said spring strip.

8. In electrical contacting apparatus of the type described, a fiat strip of spring metal, the strip being provided with a resilient portion near one end of the same, means serving to anchor said one end of the strip to a fixed support. whereby the other end of the strip is free for movement in opposite directions, said strip being provided with a spring tongue intermediate its ends with the free end 01' the tongue extending toward said fixed support, and terminating short of said resilient portion, means forming a fixed abutment for the free end of the tongue, whereby said resilient portion is stressed within its elastic limit to ai'iord snap action for the strip, and means for adjusting the amount oi stress applied to said resilient portion.

9. In electrical contacting apparatus of the type described, a fiat strip 0! spring metal, the strip being provided with a resilient portion near one end of the same, means serving to anchor said one end ofthe strip to a fixed support, whereby the other end of the strip is free for ARTHUR J KERCHER. 

